During the last years of World War 2 the United States gets wind that the Germans are developing an Atomic bomb so the OSS appeals to Midwestern University Professor Alvah Jasper (Gary Cooper), the leading American physicist leading the way to Atomic power development in the United States. They ask him to go to Europe to find Dr. Polda (Vladimir Sokoloff), an atomic scientist being held by the Nazis and bring him to the United States, but he first must meet up with his old mentor from school Dr. Katerin Lodor (Helen Thimig) who tells him that Polda is in Switzerland. When Jasper alerts the OSS to rescue Lodor due to her insistence on going back to Germany, the Nazis execute her and Jasper must go to Italy in search of the scientist. In Italy he is accompanies by a group of Italian guerrilla fighters lead by an American Pinkie (Robert Alda) and a no-nonsense female fighter Gina (Lilly Palmer), someone with whom Jasper forms an immediate bond in part because he brings out the sensitive qualities in the young woman. When he locates Polda, Jasper discovers that the scientist refuses to leave because the Nazis have kidnapped his daughter in order to force him to cooperate. During their activities to obtain Poldas daughter Jasper and Gina find themselves having to go into hiding moving from safe house to safe house. When the night comes to finally get Polda and his daughter out of Italy, a gun fight ensues with all parties having to fight for their lives.